1. Field of the Invention
This invention relates generally to an electrode type, magnetically enhanced, glow discharge device used in film deposition and, more particularly, to an improved magnetron sputtering device for high rate deposition onto stationary or moving substrates.
2. Description of Prior Art
Magnetron Sputtering is a well known technique for applying a film of material to a substrate. The process involves placing a "target" comprised of or coated with the material to be sputtered into a chamber containing a low pressure gas. A negative voltage is connected to the cathode creating a low pressure gas discharge between the target and a nearby anode. Gas atoms bombard the target's surface with high energy and, through momentum transfer between the incident ions and target atoms, eject (sputter) target atoms that will condense on the substrate. The process is self-sustaining because many of the incident gas ions, rather than ejecting an atom of the material to be sputtered, create a shower of electrons that collide with neutral gas atoms and create even more gas ions. The magnetic field increases the efficiency of the electrons producing more ions when parallel to the targets surface.
A variety of magnetron sputtering devices having different geometries and using magnetic fields of various shapes to direct and guide the gas discharge have been developed. The typical magnetron sputtering devices are plagued by non-uniform magnetic fields over the sputtering surface which causes a "race track" erosion pattern on the target and reduces target utilization efficiency to typically 5% to 15%. Target utilization can be increased through target design such as specifying removal of portions that would not be sputtered and/or specifying very thin targets. These approaches have resulted in efficiencies as high as 50%. Numerous other approaches have been made to increase target utilization. One approach is to move the target with respect to the magnets. Although this approach increases target utilization, it presents additional problems. Specifically, it requires motion components which are expensive and prone to breaking down. Minimizing down time is particularly important in commercial processes. Another solution in U.S. Pat. No. 5,073,245 issued to Hedgcoth is to use a cylindrical magnetron containing a slit in its wall. This approach allows planar substrates to be coated but significantly reduces the coating rate and is best applied to thin films.